How did the US presidential campaign get to be so long?

While other countries set strict limits on the length of campaigns, American presidential races have become drawn-out, yearslong affairs. It wasn’t always this way.

Why Marco Rubio's presidential campaign strategy is considered a gamble - Los Angeles Times

2000 United States presidential election - Wikipedia

Swing state - Wikipedia

Radio host Larry Elder ends Republican presidential campaign

Why Are U.S. Elections So Much Longer Than Other Countries'? : It's All Politics : NPR

US Presidential Elections Are Absurdly Long Compared to Rest of World

Trump found an election strategy that works – so he's sticking to it, Donald Trump

Too many US moderates make a muddle for Democrats

What was the longest presidential election in US history?